Drying apparatus



July 6 1926.

R. THELEN DRYING APARATUS Filed Sept. 12, 1924 4 Sheets-Sheet l ooooooo.oooooooooooooo@ IN V EN TOR ROLF THE LE N BY N* A TTORNEYS.

Fieri July 6 1926.

- R, THELEN DRYING APPARATUS Filed Sept. l2. 1924 4 Sheets-Sheet 2INVENTOR. ROLF THEM-:pl

TORNEYS.

`Iuly 6 1926.

R. TH ELEN DRYING APPARATUS 4 sheets-sheet 5 i Filed Sept. l2 1924oooooooooooo -4/ gooooo IN V EN TOR. ROLF 'WEKEN l M A TTORNEYS.

July 6 1926.

R. THELEN .DRYING APPARATUS Filed Sept. l2 1994 4 Sheets-Sheet 4INVENTOR. .A OLI: TIPELEN Mm WTTORNEYS.

Patented July 192%.

UNITE A'strates ROLF THELEN, 0F MADISON, WISCONSIN'l DEDICATED. BY MESNEASSIGNMENTS, T0 THE GITIZENS 0F THE UNITED STATES OF AMERICA.

DRYING APPARATUS.

Application led September 12. 1924. Serial` No. 737,369.

(GRANTED UNDER THE ACT OF MARCII 3. 1883; 22 STAT. L. 625.)

This application is made under the act of March 3, 1883. chapter 142 (22Stat. 625) and the invention herein described and claimed may be used bythe Government of the United States, its officers and emloyces, and byany person in the United gtates without the payment to me of any royaltythereon. I hereby dedicate the same to the free use of. the Governmentand the people of the United States.

This invention consists in brief in subjccting the material to be driedto air currents whose path takes a spiral or helical direction incontradistinction to most drying processes in which the path of thedrying medium lies more or less in a single plane. This spiralcirculation producesa greater uniformity in the drying medium throughoutthe length ofthe drying chamber than it has been possible to secureheretofore.

It is well known that spiral circulations of certain types have beenused heretofore, thus, for instance, Letters lPatent No. 449,170, issuedto Phillips on March 31, 1891, discloses a system of drying bricks orother similar material in which the air enters the drying chamber at oneend and follows a spiral path through the chamber, finally beingdischarged'to the atmosphere at the opposite end ofthe drying chamber.This type of circulation, which may be Aclassed as an externalcirculation because the air is drawn from4 the outside, asses but oncethrough the spiral path wit in the chamber and is then discharged to theoutside atmosphere, is designed for and adapted to progressive systemsof drying. In these systems the material to be dried'enters the dryingchamber at one end and is `periodically or constantly moved toward theopposite end, emerging therefrom at the end of the drying process.

The present invention is limited specifically to compartment systems ofdrying. In these systems the material to be dried remains continuouslyin .position in the drying chamber throughout the entire period, theentire charge being loaded into the chamber at one time and likewiseremoved from the chamber at one time. This invention is further limitedto internal circulation of the drying medium. In this type ofcirculation the principal movement of the drying medium is constantlythroughout the same patin the drying medium being recirculated and usedrepeatedly. It is the common commercial practice at the present time inmany compartment systems of drying to employ a circulation of the dryingmedium which is principally in vertical planes perpendicular to thelongitudinal axis of the drying chamber. Exc-e t in so far as it isdisturbed by outside in uences, each particle of the drying medium movescontinuously in one of these planes. No positive means are provided forproducing any longitudinal circulation in the drying processes. It hasbeen found in actual full scale commercial tests that it is not possiblewith these systems to maintain uniform d Y throughout the length of t erying chamber. This lack of uniformity is especially pronounced in thecase of long chambers in which material of Widely varying moisturecontents and Widely varying drying rates is being dried rapidly.

In thoseparts of the dr 'ng chamber in which the material to bedyir'xied has become dry first, the atmosphere becomes drier and hotterthan in those portions of the dr 'n l chamber in which the material tobe rie dries more slowly. The resulting condition is disadvantageousbecause it roduces overdrying in certain portions of t e matei'iai to inconditions be dried and under-drying in other portions, ai;

The present invention overcomes these diiiculties by'producing a certainamount oi" longitudinal circulation of the. dryin medium in addition tothe normal circu ation which is commonly called cross-circulatron. Thislongitudinal circulation imposed upon eirthe cross-circulation resultsin a spira.' culation as will become evident tron detailed descriptionoit trie application oi.

invention to tivo types yot' drying chambers.

The present invention does not limit itself to specified methods ofproducing either the cross-circulation or the longitudinaleirculatioiusince its purpose can be equally well accomplished whatever.the method of produing the circulation may be. For purposes o't`illustration and to make the operation of this invention clear to thoseskilled in the art. two typical applications are presented. the firstone illustrated in Figures I and II. a ventilated natural draftcompartment kiln designed tor the seasoning of lum ber and other woodproducts, and, second, an internal tan compartment dry kiln, alsodesigned especially for the seasoning of lumber and other Wood products.

Figure I is a cross-sectional elevation of a ventilated natural draftcompartment kiln. Figure II is a longitudinal sectional elevation of thesame kiln. Figure III is a crosssectional elevation oi an internal fancompartment kiln. Figure '[V is a longitudina'l sectional elevation ot'the same kiln. Correspoi'iding parts on the four figures arecorrespondingly lettered in so vfar as possible. Letters A to 0,inclusive, apply to all tour figures Letters P. Q. and R apply only onFigures I and II. Letters S to Z. inclusive,

y Zontal.

and Nos. 1 and 2 apply only on Figures III and IV.

Referring to the figures, AA rein-osent piles of lumber to be dried. Theindividual boards `in the pile are" arranged with the long axis parallelto the longitudinal axis of the kiln and with the board faces hori-Suitable spaces provided between the layers of lumber permit the passageof the drying medium.

. BB represent the walls of the drying chamber.

CC are air inlet ducts.

DD are air inlet duct dampers.

EE are air outlet ducts.`

FF are air outlet duct dempers.

' GG are heating coils.

HH are steam spray lines.

ll are bunks'upon which the lumber rests.

JJ are the rails upon which the piles of lumber are moved into and outof the drying chamber.

KK are rail supports.

L is a motor.

M isy the motor pulley.

N is the belt.

O is the. driven ulley.

P is the blower 1n Figure II'.

Q is the suction duct in Figures I and II.

1t' is the discharge duct in Figures I andII.

S is the line shaft in Figures III and IV.

'ITeire line shai't bearings in Figures III and IV. l

Y'f'."U are disc lans in Figures III and IV.

'VV are cross ducts in Figures III and IV.

' IVIV are plenum chambers in Figures III and lV.

XX are plenum chamber ditfusers in Figures lll and IV.

Y is the suction box in Figure IV.

Z is the pressure box in Figure IV.

1 is the reversing switch in Figure IV.

`L is the longitudinal duet in Figures III and lV.

'lhe general arrangement of the kiln shown in Figures III and IV issimilar to that illustrated in my Patent No. 1,466,518, issued on AugustQS, 1923, with the addition ot' the part required to produce the spiralcirculation Which'is the subject of this invention.

-Thc two kilns illustrated in Figures I to lV are intended to use amixture of air and water vapor, hereinafter referred to as air,

vfor the drying medium. Super-heated steamf can. however, be used as adrying medium with any change indesign.

The kiln illustrated in Figure I and Il Yl'ollows` present commercialpractice rather closely, with the exception of the blower P and themechanism functioning with it. This blower may be of conventionaldesign, the lparticular type to be used to be determined by theindividual conditions sur-4 rounding the design. When comparatively highpressures are required a centrifugal blower is indicated. When, on theother hand, the pressures required are very low, disc or propeller fanscan be used to ood advantage. The blower illustrated is o thecentrifugal type. It is driven from the motor L through the pulleys Mand O and the belt N: A suction duct Q extends from one endeof the kilnto the suction side of they blower and a discharge duct R extends fromthe pressure side of the blower to the other end of the kiln. When theblower is in operation it draws air from one end of the kiln anddischarges it to the other end of the kiln, producing a longitudinalcirculation.

This circulation, combined with the erosscirculation produced in theusual manner as will be described later, produces a resultantcirculation of spiral form.V The specific effeet of this spiralcirculation is a continual mixing of the air from end to end of thekiln. This avoids the formation of hot spots and cold spots in the kilnand thus produces more uniform drying. A

The detailed operation of the kiln shown in Figures I and II is asfollows:

After the kiln has been loaded and closed, the blower P is put intooperation, steam is turned into the heating coil G, the temperature ofthe kiln is regulated and controlled by the control of the steam supplythrough the heating coils. This control may be manual or automatic asdesired. Control of the humidity ofthe air in the kiln is secured by themanipulation of the air inlet duct Cia dampers and the air outlet ductdampers and by regulation of the supply of steam to the steam spraylines. It is customary to open the dampers sufficiently to maintain thehumidity below the desired point under ordinary lumber dryingconditions. The atn'iosphere outside oi the kiln contains less moistureper cubic foot than that within thel kiln; therefore, the humidity ofthe air in the kiln can be reduced by mixing with it the air fromthe'outside atmosphere. Air may enter the kiln through the air inletducts and escape from the kiln through the air outlet ducts. y

Having secured the desired setting of the dampers the humidity of theair of the kiln may be raised by admitting steam to the steam spraylines, which discharge the steam downward as indicated in Figure I.

Control of this steam supply may be manual or automatic as desired. Thesteam sprays issuing from the steam spray line tend to produce adownward air circulation as indicated by the arrows. This circulation isintensified by the action et the heating coils which tend to make theair rise in the space between the rows of lumber piles and by thecooling eiiect of the e evaporation of moisture from the wood. When theside walls of the kiln are exposed to the outside atmosphere the coolingetfect produced by them also tends to increase the circulation of theair in the kiln. The resultant circulation, commonly termed crosscirculation, is in the plane et Figure I and in the general directionindicated by the arrows. The discharge of air from the discharge duct isproducing a slight plenum at the end of the kiln opposite the dischargeend of the duct and the withdrawal ot' air throughout the suction duct Qproduces a slight `vacuum at the other end of the kiln. sult is amovement of air from the plenum toward the vacuum. This longitudinalmovement superimposed upon the cross-circulation I have termed thespiral circulation.

It is not anticipated that the resulting eirculation will be true spiralnor. is it necessary, to accomplish the purpose et. the invention, thatit be so. The principal purpose oi"A the invention is to produce greateruniformity in the drying medium and this is accomplishedsatisaetorilyeven when the nath oi'i'the air particles is not a truespiral. i The iriln illustrated in Figures III and IV follows veryclosely the detailed construction illustrated and described in myFai/ent No. Lfithl, With the exception et the iongit-udinal duct, thesuctionbox and assure box. The detailed construction ian il in Figure IVdie the in'essure'l" a che The obvious recated by the arrows. Thispressure box communicates with the longitudinal duct, and the airdischarged from the fan passes through the longitudinal ducts into thesuction box Y from which it is drawn through the disc fan U at the letthand of the kiln as illustrated in Figure IV. This action, coupled withthe cross-circulation normally produced by the fans creates alongitudinal mixing of the air, which I have termed the spiralcirculation. When the direction of rotation of the fans is reversed thedirection of the air movement in the longitudinal duct is also reversedand the cross-circulation as illustrated by the arrows in Figure III isreversed. The pressure box Z is then under vacuum and the suction box Yunder a slight pressure. Likewise, theV plenum chambers WW are under aslight vacuum and the cross ducts V serve to conduct the air` from thefans to the heating coils instead ot from the heating coils tothe fans.The detailed operation is similar to the operation of the kilnillustrated in Figures l and II. Control of temperature and humidity maybe had in precisely the same manner. The method of producing theeirculation is different trom the one previously described in that theprincipal circulation is produced by means of disc fans. This operationis described in detail in my Patent No. 1,466,518, already referred to.When the circulation of the air is as indicated by the arrows in FigureIII' all of the fans except the left hand one` Figure IV, draw air fromthe heating coils through the cross duet. The air passes fromall of thefans except the right hand one, Figure IV, into the plenum chambersthrough the plenum chamber ditl'users upward between two rows ot lumberpiles. laterally outward and downward to the heating coils, asillustrated. The right hand fan, Figure IV. discharges into thelongitudinal duct to the pressure box and the lett hand fan, Figure IV,draws air from the longitudinal duct to the suction box. When thedirection of rotation of the shaft and the fans is reversed the airmovement through the longitudinal duct is from left to right and thedirection of the circulation through the lumber is opposite to thatillustrated in Figure III.

The longitudinal circulation produced by the action et the end fans asjust described has precisely the same etl'ectas thel longitudinalcirculation produced by the blower P in the kiln illustrated in FiguresI and II. This eect is in brief the longitudinal mixing et the air' inthe kiln which results in a greater degree of uniformity of the air thancan be obtained without such longitudinai mixing.

Having :uily described this invention and n how it can be appiied in twotypical f original:

Ye ii 1. In u drylkiln adapted to compartment Charge duct adapted towithdraw air from operation, means 'for producing :1 spiral cirthe kilnat one end and to discharge Suid culation of air in said kiln` and meansfor uir into said kiln ut the opposite end, and 10 maintaining aiunilmmtemperature and hu means for maintaining a uniform tempera miditythroughout the kiln. ture und humidity throughout the kiln.

2. In a dry kiln adapted to Compartment Aug. 1Q, 1924. operation, :1blower, n suction duct, a dis- ROLF THELEN.

